Generic coating systems are generally called "low e" (low emissivity) systems. Such coating systems, which are applied for example to flat glass, serve to admit light in the visible spectrum but reflect longer-wavelength thermal radiation. When such flat glass is used in window glazing, it makes an advantageous contribution toward minimizing radiant heat loss from a room through glass windows.
Conventional low-e systems consist basically of the following succession of coatings: substrate/metal oxide/metal/metal oxide.
Such a low-e coating system is described, for example, in German Patent 42 11 363. The actual functional coating is the metal layer which consists of metals with a very low coefficient of radiation emission. Usually the metal coating consists of silver, gold or also copper, and alloys of these metals. The metal oxide layers serve as anti-reflective coatings and at the same time they serve to protect the metal coating against mechanical and/or chemical environmental action. Also provided are multi-layer protective coatings which increase resistance to environmental influences in generic low-e coating systems.
On account of the increasingly stringent requirements as regards the optical and energy parameters of low-e coating systems and their required resistance to environmental influences, it has been found that conventional coating systems no longer satisfy these requirements. Resistive coatings consisting of indium-tin-oxide (ITO) are known, which have emissivities between 0.15 and 0.13. One disadvantage of the use of low-e coating systems using such ITO coatings is that large-scale architectural glass applications are very expensive due to the extremely high material cost of indium. As an alternative, low-e coatings made from tin oxide are used, which for reasons of cost are applied to the support material pyrolytically and have an emissivity of 0.4.
The invention is addressed to the problem of creating a low-e coating system of the kind described above, which will have improved resistance to chemical and/or mechanical action and avoid the deficiencies of the known technical solutions.